Coal tar is a generic name given to one of the byproducts formed when coal is distilled to make coke and/or gas. Coal gasification was generally accomplished by any one of three processes: carbonization, water gas, and carburetted water gas. Occasionally, oil was used as the feedstock, but the basic process was similar to that using coal. The carbonization processes, also called coking processes, destructively distill the coal feedstock. Generally, the coal tar produced is differentiated by its mode of production--either a high temperature or low temperature process. High temperature coal tars are the condensation products obtained by the cooling of the gas evolved at processing temperatures of greater than about 700.degree. C. and up to about 1350.degree. C. Typically, temperatures for the low temperature process ranged from about 200.degree. C. to about 700.degree. C. Current production of coal tars world-wide is closely linked with steel production due to the requirement for coke in the steel making process. Estimates for world production of crude coal tars range from about 15-20 million tons. In addition to the current production of coal tar there exists substantial quantities of coal tar waste at various sites. These sites contain the coal tar either in waste vessels or in the form of contaminated soil or water.
Coal tars contain various amounts of hazardous and toxic materials such as polynuclear aromatic (PNA) hydrocarbon compounds. The presence of these PNA compounds creates concerns relating to potential exposures to the coal tar for workers and the population at large. The bioavailability of the coal tar raises issues as to the carcinogens present in the coal tar. Ways for decreasing the bioavailabilty of these PNA compounds found in coal tar are therefore needed.
A need exists to develop a way of reducing the potential bioavailability of the PNA compounds found in a coal tar sample without creating a further waste material. A useful solution would be one in which the energy value of the coal tar could be utilized.